Sliding doors are frequently installed in several types of vehicles including passenger vans and, more prominently, minivans. In minivans, the right side passenger door or the right side passenger door and the left side passenger door are slidable in tracks formed in the body of the vehicle. These doors provide access to the passenger compartment of the vehicle via a relatively wide opening.
Sliding doors should seal off the environment such as water, air, and noise. Accordingly, the door structure must be rather rigid and also must meet the safety limitations of the Federal Motor Vehicle Safety Standard (FMVSS214) which requires that the door provide a specified degree of protection from intrusion into the passenger compartment for occupants of the vehicle upon side impact. In order to achieve the strength and stiffness needs for the door and to meet the minimum safety requirements, the doors are typically fashioned from thick and strong components formed from steel. These currently available steel sliding doors are heavy, over about 44 pounds for a DiW (door in white), and relatively thick, typically about 120 mm in cross-section. Lighter weight metals such as aluminum are generally unsuitable for use at this thickness due to manufacturing difficulties. If a steel door were made thinner to reduce its weight, the resulting structural performance would be unacceptable.
An additional drawback to conventional heavy sliding doors is that they are difficult to open and close, especially when the vehicle is parked on a hill, and need a correspondingly heavier mechanism to retain the door in an open position. For smaller individuals, including children, conventional sliding doors are prohibitively difficult to open and close. Some sliding doors are equipped with motors for power operation of the door. Power driven sliding doors overcome some of the difficulties experienced by certain individuals in opening and closing the doors, however the weight of the doors remains problematic for both the power requirement for the door motors and for the overall vehicle weight.
Conventional steel doors are typically manufactured from an inner panel and an outer panel of steel. The steel panels provide structural strength for the door and act as panels for mounting of door hardware as well as serve an ornamental function. The peripheries of each of the inner and outer panels include a U-shaped embossment above the beltline of the door. These embossments are aligned with the openings of the U-shapes facing each other to form a box beam at the periphery of the assembled door. The inner panel and the outer panel are joined together below the beltline along their peripheries with a gap maintained between the inner and outer panels in the central portion of the door. A plurality of tabs integrally formed with the inner panel is bent in a direction away from the inner panel. The ends of the tabs abut the inside surface of the outer panel thereby creating stiffening bridges between the inner panel and the outer panel. The gap between the inner and outer panels is sized to allow for insertion and future maintenance of the door handle and lock hardware between the inner and outer panels of the door and also to provide adequate structural stiffness of the door. Hence, the cross-sectional thickness of a conventional steel door is typically over 120 mm which constrains the use of lighter materials such as aluminum. A further difficulty associated with conventional doors is that the available interior space of the vehicle is diminished by the thickness of the doors.
Numerous components such as the hardware for the door handle and the door lock and stereo speakers are inserted in the gap between the inner and outer panels through cutouts in the inner panel of the door. Hence, the gap between the inner and outer panels must be sufficiently large to accommodate the door hardware and other vehicle accouterments. Installation and maintenance of these components is cumbersome and requires specialized techniques and tools for accessing the gap between the inner and outer panels.
In an attempt to reduce the weight of vehicle body panels, certain body panels have been made from lightweight materials such as aluminum and plastic. For example, U.S. Pat. No. 5,449,213 discloses an aluminum movable liftgate having a tubular frame sandwiched between a pair of inner panels and a pair of outer panels. The frame functions as the load bearing structure for the liftgate, however, there is no provision in the disclosed panel for the hardware or for the contour and other design requirements of a sliding door installed on the side of a vehicle.
Accordingly, a need remains for a thin, lightweight sliding door which maximizes the vehicle interior space and which also allows ready access to the door hardware.